Seasonal outlook of the East Asian Summer in 2015 Motoaki Takekawa Tokyo Climate Center Japan Meteorological Agency May th FOCRAII 1

Oceanic conditions in April 2015 SST anomalies Sub-surface sea temperature anomalies in the equatorial Pacific May th FOCRAII 2 # The distribution of SST anomalies shows an El Nino like condition. # Positive anomalies are dominant in sub-surface sea temperature along the equatorial central and eastern Pacific

zonal wind stressOcean Heat Content SST Time-Longitude cross section along the equator Inter-seasonal evolution of oceanic conditions # Strong westerly bursts excited warm Kelvin waves with large amplitude. # Kelvin waves have reached the west coast of South America.

Predicted oceanic conditions in JJA (1) SST anomalies Prediction accuracy ( verification result by the 30-year hindcast ) Anomaly correlation coefficients May th FOCRAII 4 # El Niño conditions will redevelop. # Prediction skill is pretty good. 95% significant

Predicted sub-tropical circulation in JJA (1) May th FOCRAII 5 Precipitation and anomalies Prediction accuracy ( verification result by the 30-year hindcast ) Anomaly correlation coefficients 95% significant # Distribution of precipitation shows characteristics of El Niño events. # Prediction skill is good. Active convection anomalies Suppressed convection anomalies

Predicted sub-tropical circulation in JJA (2) 200hPa velocity potential and anomalies May th FOCRAII 6 # Anomaly pattern of 200hPa velocity potential shows characteristics of El Niño events. Precipitation and anomalies Large scale convergence anomalies Large scale divergence anomalies

Predicted sub-tropical circulation in JJA (2) May th FOCRAII 7 El Nino composite : 200hPa stream function anomalies Cyclonic circulation anomalies Wave train 200hPa stream function and anomalies # Anomaly pattern of stream function shows typical patterns which were observed when El Niño events occurred.

Predicted sub-tropical circulation in JJA (2) 200hPa stream function and anomalies Prediction accuracy ( verification result by the 30-year hindcast ) Anomaly correlation coefficients Apr th FOCRAII 8 # The CGCM has significant skill in not only the Rossby response, but also zonal north-south shift of sub- tropical jet. 95% significant

850hPa stream function and anomalies Cyclonic circulation anomalies Anti cyclonic circulation anomalies Predicted sub-tropical circulation in JJA (3) May th FOCRAII 9 # Anomaly pattern of stream function shows typical patterns which were observed when El Niño events occurred. El Nino composite: 850hPa stream function anomalies

Interannual variation of summer mean temperature May th FOCRAII 10 Tropospheric thickness temperature Below normal Near normal Above normal Northern Japan 028 Eastern Japan 136 Western Japan 136 Okinawa 037 Temperature ranks during recent 10years ( ) # Hot summer has been dominant in Japan recently. # warming tendency is seen in tropospheric thickness temperature.

11-13 May th FOCRAII 11 Predicted sub-tropical circulation in JJA (4) Tropospheric thickness temperature(JJA hPa), Overall temperatures in the troposphere are expected to be higher than normal, particularly on the lower latitudes side of the sub tropical jet.

summary of Numerical prediction and its interpretation ・ It is likely that El Niño conditions will redevelop by the boreal summer ・ Predicted atmospheric circulation anomalies are as follows, Asian summer monsoon will be generally weaker than normal. The sub-tropical jet will shift southward compared to the normal latitude. This means weak Tibetan high. North pacific high will not extend to north, but around southeast of Japan, it will be not weaker than normal. These characteristics are consistent with those observed during past El Niño events. ・ Additionally, it is necessary to consider that overall temperatures in the troposphere are expected to be higher than normal, particularly on the lower latitudes side of the sub tropical jet, reflecting recent warming tendency and high SSTs in the equatorial Pacific May th FOCRAII 12

Schematic chart of outlook for East Asian circulation in JJA May th FOCRAII 13

High Normal Low Probability forecast of seasonal mean temperature for JJA 2015 in Japan Northern Japan Eastern Japan Western Japan Okinawa & Amami May th FOCRAII Climatology 33 Summer mean temperatures are expected to be both near normal and above normal with 40% probabilities in eastern Japan.

Probability forecast of seasonal precipitation for JJA 2015 in Japan Northern Japan Eastern Japan Western Japan Okinawa & Amami May th FOCRAII Climatology 33 Above normal Normal Below normal Summer precipitation amounts are expected to be both near normal and above normal with 40% probabilities in northern Japan.

Thank you May th FOCRAII 16

11-13 May th FOCRAII hPa height 850hPa temperature SLP Predicted sub-tropical circulation in JJA (4)

Predicted sub-tropical circulation in JJA (3) Rossby Response May th FOCRAII hPa stream function and anomalies Prediction accuracy ( verification result by the 30-year hindcast )

Predicted sub-tropical circulation in JJA (3) May th FOCRAII 19 Precipitation and anomalies Prediction accuracy ( verification result by the 30-year hindcast ) Anomaly correlation coefficients 95% significant # above normal rainfall is predicted around Philippines. # These anomalies have significant skill.

Linear Regression SST in (-5-5, ) and rain JJA May th FOCRAII 20 Precipitation and anomalies JMA’s CGCM by the 30-year hindcast Intial; April # Meanwhile, JMA’s CGCM probably tend to predict more active convections around Philippines in El Nino conditions. JRA25